PCT International Patent Publication No. WO 03/058 167 describes a rotation-rate sensor having a substrate and a Coriolis element, the Coriolis element being excitable to vibrate in parallel to a first axis, a deflection of the Coriolis element being provided in response to a Coriolis force in a second axis perpendicular to the first axis, and the rotation-rate sensor having force-mediating means between the substrate and the Coriolis element in the form of compensation structures provided for compensating for quadrature. The Coriolis element includes a seismic mass which has a plurality of cutouts. The compensation structures include first and second electrodes which are anchored to the substrate and project perpendicularly to the substrate surface, each into a cutout of the frame. The inner periphery of the cutout is asymmetrical in shape, so that, by suitably connecting the first or the second electrodes, a first or second compensation force of the frame relative to the substrate is produced in the one direction in parallel or, in the other direction, antiparallel to the detection direction, the force increasing proportionally to the deflection of the driving vibration. Therefore, to generate the particular compensation force, only one of the first and second electrodes is connected in each case, while the other one of the first and second electrodes is not connected or is only connected by application of a weak voltage. These particular compensation forces are able to compensate for an unwanted transversal force on the frame in parallel to the detection direction, referred to in the following as quadrature force, that is produced by the driving motion (quadrature compensation). Such quadrature forces arise due to sensor design imperfections inherent in the manufacturing, and they lead to a modulation of the Coriolis detection signals by the drive frequency and thus to unwanted offset signals in the detection branch.
The quadrature is disadvantageously altered by external influences (such as temperature variations or substrate deformations caused by package stress, for example), so that it is necessary to raise or reduce the first and second quadrature voltage accordingly to circuit-connect the first and second electrodes. However, this also leads to a change in the effective spring stiffness of the detection structure, which is dependent, on the one hand, on the mechanical stiffness of the detection springs, on the other hand, however, also on the electrical connection of all electrodes in the detection circuit, thus, in particular, also on the quadrature voltages, whereby the resonant frequency of the detection mode shifts, in turn. This is referred to in the following as positive feedback. For that reason, to permit operation of the rotation-rate sensor at full resonance, i.e., for the detection frequency to equal the drive frequency, the detection voltages must be adapted accordingly. Particularly in view of relatively substantial positive feedback effects, in combination with manufacturing tolerances, the result is that an operation of the rotation-rate sensor at full resonance cannot be ensured at all times, so that the detection sensitivity, respectively the signal-to-noise ratio of the rotation-rate sensor is degraded.